Manufacturing of optical fibers with symmetry-breaking longitudinal protrusions

Abstract

A method of manufacturing an optical fiber is provided. The method involves providing a fiber preform with an active core and a pump-guiding cladding, and assembling one or more side rods to the fiber preform. The side rods extend longitudinally along an outer surface of the pump-guiding cladding. The resulting fiber preform assembly is drawn into the optical fiber. Each side rod defines a longitudinal protrusion extending along the optical fiber. Each longitudinal protrusion may have a cross-section forming a middle bump projecting radially away from the outer surface of the pump-guiding cladding and smooth transition regions with this outer surface of the pump-guiding cladding on opposite sides of the middle bump.

1 . A method of manufacturing an optical fiber, comprising:
 a) providing a fiber preform comprising an active core and a pump-guiding cladding surrounding the core;   b) assembling one or more side rods to the fiber preform, therefore forming a fiber preform assembly, each of the side rods extending longitudinally along an outer surface of the pump-guiding cladding; and   c) drawing the fiber preform assembly into said optical fiber such that each of the side rods defines a longitudinal protrusion extending along said pump-guiding cladding.   
     
     
         2 .- 4 . (canceled) 
     
     
         5 . The method according to  claim 1 , wherein the assembling of step b comprises distributing the plurality of said side rods non-uniformly around the fiber preform. 
     
     
         6 . (canceled) 
     
     
         7 . The method according to  claim 1 , wherein a ratio of a diameter of each side rod to a diameter of the fiber preform is larger than 0.02. 
     
     
         8 . (canceled) 
     
     
         9 . The method according to  claim 1 , wherein the assembling of step b. comprises fusing each of the side rods to the outer surface of the pump-guiding cladding. 
     
     
         10 . The method according to  claim 1 , wherein the assembling of step b. comprises partially fusing each of the side rods to the outer surface of the pump-guiding cladding. 
     
     
         11 . The method according to  claim 1 , wherein the assembling of step b. comprises providing a holder holding the side rods along the outer surface of the pump-guiding cladding. 
     
     
         12 .- 13 . (canceled) 
     
     
         14 . The method according to  claim 1 , wherein the drawing of step c is performed at a temperature sufficient to fuse the one or more side rods to the outer surface of the pump-guiding cladding. 
     
     
         15 . The method according to  claim 1 , further comprising surrounding the optical fiber with at least one outer cladding. 
     
     
         16 .- 21 . (canceled) 
     
     
         22 . An optical fiber manufactured by the method according to  claim 1 . 
     
     
         23 . The optical fiber according to  claim 22 , wherein each longitudinal protrusion has a cross-section forming a middle bump projecting radially away from the outer surface of the pump-guiding cladding and smooth transition regions with said outer surface of the pump-guiding cladding on opposite sides of said middle bump. 
     
     
         24 . The optical fiber according to  claim 23 , wherein the optical fiber has a circular perimeter defined by the outer surface of the pump-guiding cladding, each longitudinal projection has a height ratio R defined by a radial height of the middle bump with respect to the circular perimeter of the optical fiber over a diameter of the optical fiber at said circular perimeter, said height ratio R of each longitudinal protrusion being smaller than 0.20. 
     
     
         25 . The optical fiber according to  claim 24 , wherein the height ratio R of each longitudinal protrusion is smaller than 0.06. 
     
     
         26 .- 27 . (canceled) 
     
     
         28 . The optical fiber according to  claim 23 , wherein the smooth transition regions of each longitudinal protrusion have a radius of curvature greater than 0.1 m. 
     
     
         29 . (canceled) 
     
     
         30 . The optical fiber according to  claim 22 , having a cladding pump absorption factor greater than 0.5. 
     
     
         31 .- 32 . (canceled) 
     
     
         33 . The optical fiber according to  claim 22 , having a resistance to pulling or bending greater than 100 kpsi. 
     
     
         34 . (canceled) 
     
     
         35 . The optical fiber according to  claim 22 , wherein stresses around each of the longitudinal protrusions are smaller than 200 MPa. 
     
     
         36 .- 38 . (canceled) 
     
     
         39 . The optical fiber according to  claim 22 , having an average core-cladding concentricity error smaller than 0.4%. 
     
     
         40 . An optical fiber comprising:
 an active core;   a pump-guiding cladding surrounding the core and having an outer surface; and   one or more longitudinal protrusions extending along said pump-guiding cladding, each longitudinal protrusion having a cross-section forming a middle bump projecting radially away from the outer surface of the pump-guiding cladding and smooth transition regions with said outer surface of the pump-guiding cladding on opposite sides of said middle bump.   
     
     
         41 .- 43 . (canceled) 
     
     
         44 . The optical fiber according to claim  42 , wherein the plurality of longitudinal protrusions are non-uniformly distributed around the pump-guiding cladding. 
     
     
         45 .- 52 . (canceled) 
     
     
         53 . The optical fiber according to  claim 40 , wherein the smooth transition regions of each longitudinal protrusion have a radius of curvature greater than 0.1 m. 
     
     
         54 .- 64 . (canceled)